1. Field of the Invention
The present invention relates to an optical scanner to be used in a writing optical system of an image forming apparatus such as a digital copier or a laser printer, and particularly to a technique for positioning and fixing a light emitting element having a plurality of light beams.
2. Description of the Related Art
Heretofore, image forming apparatuses have been widely known in which lasers are used as light sources in electrophotographic image formation. As a technique for adjusting the pitch of beams emitted from a plurality of laser diodes, the following technique has been disclosed in, e.g., “Patent Literature 1” and “Patent Literature 2”: a light source unit having laser diodes mounted thereon is rotated to be adjusted, and then the light source unit is fixed to a light source mounting portion with screws.
However, in the above-described technique, the light source unit 1 needs to be pressed by a pressing force A against a reference plane, for example, a side wall 7a of an optical housing 7, of the light source mounting portion with a turning jig at the time of rotational adjustment (see FIG. 10). At this time, the pressing causes the inclination of the light source mounting portion, as shown by dotted line in FIG. 10. In the case where adjustment and fixation are performed in a state in which the inclination exists as described above, when the turning jig is detached after the adjustment and the fixation, the inclination of the light source mounting portion returns to an original state. Accordingly, the amount of inclination of the light source mounting portion at the time of the adjustment differs from that after the fixation, and the inclination of the optical axis occurs. Thus, the distance and position of projected light are changed. In the case of a writing system, there has been the problem that the quality of a written image is lowered.
Accordingly, as a technique for preventing the inclination of the light source mounting portion, the following technique has been disclosed in, e.g., “Patent Literature 3”: reinforcing ribs are placed near an opening provided in a side wall of an optical box to which the light source unit is mounted, thereby locally reinforcing the rigidity of the side wall of the optical box.
Moreover, as a technique for adjusting the pitch of the beams emitted from a plurality of laser diodes, the following technique has been disclosed in, e.g., “Patent Literature 4”: by rotating a light emitting element while pressing the light emitting element against an optical housing, the beam pitch is adjusted, and the light emitting element is fixed in place.
Moreover, as a technique for preventing a laser diode from falling off, the following technique has been disclosed in, e.g., “Patent Literature 5”: nails are provided near an entrance of a mounting hole for a laser diode, and the insertion of a laser diode into the mounting hole causes a flange portion of the laser diode to be fixed in place with the nails. In this technique, distortion by press-fitting does not occur, and therefore another member is not needed. Thus, cost reduction can be achieved.
However, in the technique disclosed in “Patent Literature 3”, the rigidity is locally enhanced, but the influence of the inclination is not completely eliminated. With regard to the accuracy of beam pitch on a photoreceptor, errors must be extremely severely managed to such an extent that the permissible error is several micrometers or less. Accordingly, sufficient accuracy cannot be achieved.
Moreover, in the technique disclosed in “Patent Literature 4”, as shown in FIG. 28, even if the beam pitch is adjusted, there has been the problem that a side wall 7a of an optical housing 7 is inclined inward as indicated by broken lines in FIG. 28 by the action of a pressing force A of a turning jig holding a light emitting element 9, and therefore the adjustment of the beam spacing is not correctly performed (reference numeral 7b denotes a reference plane to be used to mount the light emitting element 9). In particular, recently, relatively easily deformable optical housings made of resin have been frequently used for the sake of cost reduction and weight reduction. Accordingly, when a pressing force of a turning jig is released after adjustment, an optical housing returns to an original shape, and the optical axis and the beam pitch change from those at the time of the adjustment.
Moreover, in the technique disclosed in “Patent Literature 5”, the nails for fixation are placed inward of the flange portion of the laser diode. Accordingly, in either of the case where the laser diode is inserted or the case where the laser diode is detached, loads are placed on the nails, and the nails may be broken. The Patent Literatures as mentioned above are listed below.